Borrego Valley Groundwater Conditions Completed
Groundwater is effectively the sole source of water supply for Borrego Valley, California. By the mid-2000s, agriculture, recreation (predominantly golf courses), municipal uses, and the Anza-Borrego Desert State Park required about four times more water than is available through natural recharge. As a result, the U.S. Geological Survey began a cooperative study of the Borrego Valley with the Borrego Water District (BWD) in 2009. The purpose of the study was to develop a greater understanding of the hydrogeology of the Borrego Valley Groundwater Basin and provide tools to help evaluate the potential hydrologic effects of future development.
Groundwater Availability | Groundwater Quality | References
The Borrego Valley
The Borrego Valley is a small valley in the northeastern part of San Diego County, about 60 miles northeast of San Diego. Native Americans inhabited the valley and utilized the springs and surface water sources from the nearby mountain ranges. Cattlemen began homesteading the Borrego Valley in about 1875. The first successful modern well was dug in 1926, which quickly led to irrigation farming. By then, the valley's population center, the small desert community of Borrego Springs, included a post office, a small general store, and a gas station. Historically, the principal source of water for the valley has been groundwater. The Anza-Borrego Desert State Park, which encompasses 600,000 acres in and around the Borrego Valley, was established in 1933. The park was established to protect this unique desert environment. The military presence of both the Army and Navy during World War II brought the first paved roads and electricity to Borrego Springs. After the war, land developers subdivided the area, attempting to create a resort community supported by an increase in tourism generated by the Anza-Borrego Desert State Park.
Currently, about 30 percent of the land is used for agriculture and recreation, about 69 percent is natural vegetation, and 1 percent is municipal land use (California Department of Water Resources, 1998). The natural vegetation on the valley floor is a diverse variety of desert flora. One of the iconic species found within the Borrego Valley is Washingtonia filifera, the California Fan Palm, which is a lower risk/near-threatened species and the only palm native to the western United States (Hogan, 2009).
Residential and commercial development is relatively minor; the population of the village of Borrego Springs, located in the middle of the Valley, was 3,429 at the 2010 census, up from 2,535 at the 2000 census (U.S. Census Bureau, http://factfinder2.census.gov/main.html, accessed June 27, 2011). Tourism is a major industry in Borrego Springs, which has four public golf courses, a tennis center, and horseback riding, among other facilities and attractions available to visitors. The village is a popular destination for "snow birds" that migrate annually from the colder climates in winter to enjoy the sunshine of this desert community.
Groundwater Availability
From the time the valley was first settled, groundwater has been the main source of water. Before the valley was developed, long-term natural recharge and discharge were in dynamic equilibrium. Once the valley was settled, substantial changes to the amount, distribution, and type of discharge from the valley began. The valley has gradually been transformed to include farms, residential homes, and golf resorts (California Department of Water Resources, 1984b). Since the early 1950s, pumping for irrigated agriculture, golf courses, residential and commercial uses, has required more groundwater than is available through natural recharge. Groundwater-level declines during 1945-2010 were as much as 2 feet per year in wells in the northern part of the valley, where groundwater is intensively pumped for irrigation agriculture.
In an effort to address the issue of groundwater availability in the valley, the Borrego Valley Hydrologic Model (BVHM) was developed (Faunt and others, 2015). The BVHM is a tool that can be used to evaluate the effects of temporal changes in recharge and pumping and to compare the relative effects of different water-management scenarios. Overall, the development of the BVHM, along with data networks and hydrologic analysis provide a basis for assessing groundwater availability, and potential water-resource management guidelines.
Groundwater Recharge
Groundwater recharge to the Borrego Valley comes from both natural and human sources. The primary source of natural recharge to the basin is infiltration from the ephemeral streams and washes emanating along the western and northern boundaries of the valley. The source of water to these streams is precipitation and runoff from the San Ysidro and Santa Rosa Mountains (fig. 1). Other potential sources of natural recharge include direct infiltration of precipitation, lateral groundwater underflow from adjacent bedrock areas and groundwater basins, and groundwater flow across the Coyote Creek fault, all of which probably are small or negligible in quantity.
New, human-induced sources of recharge accompanied development in the basin, including irrigation-return flow from agricultural fields, golf courses, and municipal lawns, and infiltration of treated and untreated wastewater.
Groundwater Discharge
Before the Borrego Valley was developed by settlers and farmers, groundwater discharge consisted of evapotranspiration by mesquite trees and other native vegetation, discharge from Borrego Spring (Mendenhall, 1909), and lateral groundwater underflow that left the basin across the southeastern boundary of the valley. Currently, groundwater discharge occurs in three primary forms:
- evapotranspiration in areas where the water table is shallow and direct uptake from plants (mostly in and around the Borrego Sink—a topographic low where the water table was within 10 ft of land surface);
- a small amount of seepage from the southern end of the basin;
- groundwater pumping for agricultural, recreational, and municipal uses.
Natural discharge from evapotranspiration ranges from approximately 6,500 acre-ft/yr prior to development to virtually zero in the last several decades (1990-2010) because the groundwater levels in the basin dropped below the reach of the mesquite in the basin. Underflow out the southern end of the basin is small and relatively stable over time, at about 500 acre-ft/yr. Groundwater pumpage for agriculture and recreation was estimated on the basis of irrigated acreage and consumptive-use data. Values of pumpage for municipal supply were compiled from water-use records. Estimated combined annual agricultural, recreational, and municipal pumpage peaked at around 19,600 acre-ft from 2005 to 2010.
Change in Groundwater Availability
The calibrated BVHM was used to simulate the response of the aquifer to six future 50-year (2011 to 2060) pumping scenarios. Two of these scenarios (1 and 6) are summarized here. Results from Scenario 1 (continuation of current (2010) annual pumpage) indicated that the drawdown observed since pre-development would continue, with a total depletion in groundwater storage of about 1,000,000 acre-ft by 2060. Consequently, the water table declines into the middle aquifer in some areas. Because of the lower hydraulic conductivity and storage properties of the middle aquifer relative to the upper aquifer, continued pumping at these rates would result in larger, more rapid groundwater-level declines in the future and possibly a reduction in groundwater quality.
The California Sustainable Groundwater Management Act (SGMA) of 2014 requires basins to reach sustainable yield. As human activities change the system, the components of the water budget (inflows, outflows, and changes in storage) also will change and must be accounted for in any management decisions. Because there currently is little captured recharge or discharge, in this system 'sustainability' is a maximum amount of discharge that avoids future groundwater-storage depletion, and is being simplified and equated to this average recharge. In the long run, the average change in groundwater storage would be negligible when the basin is operated at the sustainable level; however, groundwater levels and storage changes would continue to fluctuate as they have historically with climatic variability.
In order to simulate a realistic approach for meeting SGMA requirements on the 20-year SGMA timeline for implementation, in Scenario 6 in the BVHM, municipal and recreational pumpages both were reduced to 50 percent of current (2010) rates, and agricultural pumpage was reduced to 40 percent of current rates. These reductions were applied linearly over 20 years and continued for the next 30 years until 2060. With these reductions, at 2060, recharge approximates discharge. Simulated drawdowns are approximately 50 feet, over a broad part of the basin. Drawdown and groundwater storage losses continue in areas where agricultural, recreational and municipal pumping occurs. In the long run, groundwater levels would stabilize and would not decline as they do in the Scenario 1 simulation which had continued significant groundwater-level and storage declines. However, changes in groundwater storage would fluctuate with climatic variability.
Assessment of Groundwater Quality in the Borrego Valley
The quality of water in the Borrego Valley is a concern because of the basin's reliance on groundwater for agricultural, recreational, and municipal supply. Groundwater quality can be affected by land-use activities occurring at or near land surface. These activities include irrigation of vegetated landscapes and the use of septic systems to dispose of wastewater. Groundwater quality can also be affected by declining water levels, as there is the potential to change the distribution of flow from underlying aquifers to wells. Historic and current water-quality data was used to determine which constituents had relatively high concentrations compared to water-quality thresholds and if these constituent concentrations were changing in response to declining water levels. Age-dating isotopes (tritium and carbon-14) were analyzed to determine if modern groundwater recharge is occurring in the Borrego Valley. Major findings of groundwater-quality portion of this study are the following:
- Historic water-quality data showed that in the upper aquifer, total dissolved solids (TDS) and nitrate as N exceeded their respective water-quality thresholds of 500 mg/L (secondary recommended CA-MCL) and 10 mg/L. Currently, the source of this nitrate is unknown.
- TDS and sulfate were the only constituents that showed increasing concentrations with simultaneous declines in water levels.
- TDS and nitrate concentrations were generally highest in the upper aquifer and in the northern portion of the Borrego Valley, where agricultural activities are primarily concentrated.
- Age-dating isotopes indicated that very little groundwater recharge is occurring under current climatic conditions and that the vast majority of natural recharge is occurring adjacent to the mountain fronts.
Borrego Valley Groundwater References
Borrego Water District, 2009. Integrated Water Resources Management Plan.
California Department of Water Resources, 1998. San Diego County Land use survey, accessed January 31, 2014, at http://www.water.ca.gov/landwateruse/lusrvymain.cfm.
California Department of Water Resources, 1984b. Evaluation of future operations of the Borrego Valley ground water basin: California Department of Water Resources Technical Information Record 1335-11-B-2, by P. Louie and H. Iwanaga.
Dawson, B.J.M., and Belitz, Kenneth, 2012. Status of groundwater quality in the California Desert Region, 2006-2008—California GAMA Priority Basin Project: U.S. Geological Survey Scientific Investigations Report 2012-5040, 110 p.
Dorsey, R.J., 2002. Stratigraphic record of Pleistocene initiation and slip on the Coyote Creek fault, Lower Coyote Creek, southern California, in Barth, A.,ed., Contributions to Crustal Evolution of the Southwestern United States: Boulder, Colorado, Geological Society of America Special Paper 365, p. 251-269.
Durbin, Timothy J.; Bond, Linda D., 1988. FEMFLOW3D; a finite-element program for the simulation of three-dimensional aquifers; version 1.0, U.S. Geological Survey Open-File Report 97-810, 338 p.
Faunt, C. C., Stamos, C. L., Flint, L. E., Wright, M. T., Burgess, M. K., Sneed, M., Brandt, J., Martin, P., and Coes, A. L., 2015. Hydrogeology, Hydrologic Effects of Development, and Simulation of Groundwater Flow in the Borrego Valley, San Diego County, California: U.S. Geological Survey Scientific Investigations Report 2015-5150, DOI: 10.3133/sir20155150
Henderson, Thomas W., 2001. Hydrogeology and Numerical Modeling of the Borrego Valley Aquifer System. Masters Thesis, San Diego State University, 520p.
Hogan, C.M., 2009. California Fan Palm: Washingtonia filifera, in Stromberg, Nicklas, ed., GlobalTwitcher.com.
Hunt, C. B. 1967. Physiography of the United States. W. H. Freeman, San Francisco, Calif. 480 pp.
Mathany, T.M., Wright, M.T., Beuttel, B.S., and Belitz, Kenneth, 2012. Groundwater-quality data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts study unit, 2008-2010: Results from the California GAMA Program: U.S. Geological Survey Data Series 659, 100 p.
Mitten, H. T.; Lines, G. C.; Berenbrock, Charles; Durbin, T. J., 1988. Water resources of Borrego Valley and vicinity, San Diego County, California; Phase 2, Development of a ground-water flow model, USGS Water-Resources Investigations Report 87-4199, 32 p.
Moyle, Jr., W.R., 1988. Water Resources of Borrego Valley and Vicinity, California: Phase 1, Definition of Geologic and Hydrologic Characteristics of the Basin, U.S. Geological Survey Open-File Report 82-855, 43p.
Netto, Steven Paul, 2001. Water Resources of Borrego Valley, San Diego County, CA. Masters Thesis, San Diego State University, 442p.
Subitzky, Seymour (editor), 1985. Selected papers in the hydrologic sciences, U.S. Geological Survey Water Supply Paper 2270, 120 p.
Thorne, James, Ryan Boynton, Lorraine Flint, Alan Flint, and Thuy-N'goc Le (University of California, Davis and U.S. Geological Survey). 2012. Development and Application of Downscaled Hydroclimatic Predictor Variables for Use in Climate Vulnerability and Assessment Studies. California Energy Commission. Publication number: CEC-500-2012-010.
U.S. Census Bureau, 2010. 2010 Census, General Population and Housing Characteristics, Borrego Springs CDP, California. Accessed http://factfinder2.census.gov/main.html on June 27, 2011.
U.S. Census Bureau, 2000. 2000 Census, General Population and Housing Characteristics, Borrego Springs CDP, California. Accessed http://factfinder2.census.gov/main.html on June 27, 2011.
Wright, M.T., Fram, M.S., and Belitz, Kenneth, 2015. Geochemical conditions and the occurrence of selected trace elements in groundwater basins used for public drinking-water supply, Desert and Basin and Range hydrogeologic provinces, 2006-11-California GAMA Priority Basin Project: U.S. Geological Survey Scientific Investigations Report 2014-5173, 48 p.
Groundwater is effectively the sole source of water supply for Borrego Valley, California. By the mid-2000s, agriculture, recreation (predominantly golf courses), municipal uses, and the Anza-Borrego Desert State Park required about four times more water than is available through natural recharge. As a result, the U.S. Geological Survey began a cooperative study of the Borrego Valley with the Borrego Water District (BWD) in 2009. The purpose of the study was to develop a greater understanding of the hydrogeology of the Borrego Valley Groundwater Basin and provide tools to help evaluate the potential hydrologic effects of future development.
Groundwater Availability | Groundwater Quality | References
The Borrego Valley
The Borrego Valley is a small valley in the northeastern part of San Diego County, about 60 miles northeast of San Diego. Native Americans inhabited the valley and utilized the springs and surface water sources from the nearby mountain ranges. Cattlemen began homesteading the Borrego Valley in about 1875. The first successful modern well was dug in 1926, which quickly led to irrigation farming. By then, the valley's population center, the small desert community of Borrego Springs, included a post office, a small general store, and a gas station. Historically, the principal source of water for the valley has been groundwater. The Anza-Borrego Desert State Park, which encompasses 600,000 acres in and around the Borrego Valley, was established in 1933. The park was established to protect this unique desert environment. The military presence of both the Army and Navy during World War II brought the first paved roads and electricity to Borrego Springs. After the war, land developers subdivided the area, attempting to create a resort community supported by an increase in tourism generated by the Anza-Borrego Desert State Park.
Currently, about 30 percent of the land is used for agriculture and recreation, about 69 percent is natural vegetation, and 1 percent is municipal land use (California Department of Water Resources, 1998). The natural vegetation on the valley floor is a diverse variety of desert flora. One of the iconic species found within the Borrego Valley is Washingtonia filifera, the California Fan Palm, which is a lower risk/near-threatened species and the only palm native to the western United States (Hogan, 2009).
Residential and commercial development is relatively minor; the population of the village of Borrego Springs, located in the middle of the Valley, was 3,429 at the 2010 census, up from 2,535 at the 2000 census (U.S. Census Bureau, http://factfinder2.census.gov/main.html, accessed June 27, 2011). Tourism is a major industry in Borrego Springs, which has four public golf courses, a tennis center, and horseback riding, among other facilities and attractions available to visitors. The village is a popular destination for "snow birds" that migrate annually from the colder climates in winter to enjoy the sunshine of this desert community.
Groundwater Availability
From the time the valley was first settled, groundwater has been the main source of water. Before the valley was developed, long-term natural recharge and discharge were in dynamic equilibrium. Once the valley was settled, substantial changes to the amount, distribution, and type of discharge from the valley began. The valley has gradually been transformed to include farms, residential homes, and golf resorts (California Department of Water Resources, 1984b). Since the early 1950s, pumping for irrigated agriculture, golf courses, residential and commercial uses, has required more groundwater than is available through natural recharge. Groundwater-level declines during 1945-2010 were as much as 2 feet per year in wells in the northern part of the valley, where groundwater is intensively pumped for irrigation agriculture.
In an effort to address the issue of groundwater availability in the valley, the Borrego Valley Hydrologic Model (BVHM) was developed (Faunt and others, 2015). The BVHM is a tool that can be used to evaluate the effects of temporal changes in recharge and pumping and to compare the relative effects of different water-management scenarios. Overall, the development of the BVHM, along with data networks and hydrologic analysis provide a basis for assessing groundwater availability, and potential water-resource management guidelines.
Groundwater Recharge
Groundwater recharge to the Borrego Valley comes from both natural and human sources. The primary source of natural recharge to the basin is infiltration from the ephemeral streams and washes emanating along the western and northern boundaries of the valley. The source of water to these streams is precipitation and runoff from the San Ysidro and Santa Rosa Mountains (fig. 1). Other potential sources of natural recharge include direct infiltration of precipitation, lateral groundwater underflow from adjacent bedrock areas and groundwater basins, and groundwater flow across the Coyote Creek fault, all of which probably are small or negligible in quantity.
New, human-induced sources of recharge accompanied development in the basin, including irrigation-return flow from agricultural fields, golf courses, and municipal lawns, and infiltration of treated and untreated wastewater.
Groundwater Discharge
Before the Borrego Valley was developed by settlers and farmers, groundwater discharge consisted of evapotranspiration by mesquite trees and other native vegetation, discharge from Borrego Spring (Mendenhall, 1909), and lateral groundwater underflow that left the basin across the southeastern boundary of the valley. Currently, groundwater discharge occurs in three primary forms:
- evapotranspiration in areas where the water table is shallow and direct uptake from plants (mostly in and around the Borrego Sink—a topographic low where the water table was within 10 ft of land surface);
- a small amount of seepage from the southern end of the basin;
- groundwater pumping for agricultural, recreational, and municipal uses.
Natural discharge from evapotranspiration ranges from approximately 6,500 acre-ft/yr prior to development to virtually zero in the last several decades (1990-2010) because the groundwater levels in the basin dropped below the reach of the mesquite in the basin. Underflow out the southern end of the basin is small and relatively stable over time, at about 500 acre-ft/yr. Groundwater pumpage for agriculture and recreation was estimated on the basis of irrigated acreage and consumptive-use data. Values of pumpage for municipal supply were compiled from water-use records. Estimated combined annual agricultural, recreational, and municipal pumpage peaked at around 19,600 acre-ft from 2005 to 2010.
Change in Groundwater Availability
The calibrated BVHM was used to simulate the response of the aquifer to six future 50-year (2011 to 2060) pumping scenarios. Two of these scenarios (1 and 6) are summarized here. Results from Scenario 1 (continuation of current (2010) annual pumpage) indicated that the drawdown observed since pre-development would continue, with a total depletion in groundwater storage of about 1,000,000 acre-ft by 2060. Consequently, the water table declines into the middle aquifer in some areas. Because of the lower hydraulic conductivity and storage properties of the middle aquifer relative to the upper aquifer, continued pumping at these rates would result in larger, more rapid groundwater-level declines in the future and possibly a reduction in groundwater quality.
The California Sustainable Groundwater Management Act (SGMA) of 2014 requires basins to reach sustainable yield. As human activities change the system, the components of the water budget (inflows, outflows, and changes in storage) also will change and must be accounted for in any management decisions. Because there currently is little captured recharge or discharge, in this system 'sustainability' is a maximum amount of discharge that avoids future groundwater-storage depletion, and is being simplified and equated to this average recharge. In the long run, the average change in groundwater storage would be negligible when the basin is operated at the sustainable level; however, groundwater levels and storage changes would continue to fluctuate as they have historically with climatic variability.
In order to simulate a realistic approach for meeting SGMA requirements on the 20-year SGMA timeline for implementation, in Scenario 6 in the BVHM, municipal and recreational pumpages both were reduced to 50 percent of current (2010) rates, and agricultural pumpage was reduced to 40 percent of current rates. These reductions were applied linearly over 20 years and continued for the next 30 years until 2060. With these reductions, at 2060, recharge approximates discharge. Simulated drawdowns are approximately 50 feet, over a broad part of the basin. Drawdown and groundwater storage losses continue in areas where agricultural, recreational and municipal pumping occurs. In the long run, groundwater levels would stabilize and would not decline as they do in the Scenario 1 simulation which had continued significant groundwater-level and storage declines. However, changes in groundwater storage would fluctuate with climatic variability.
Assessment of Groundwater Quality in the Borrego Valley
The quality of water in the Borrego Valley is a concern because of the basin's reliance on groundwater for agricultural, recreational, and municipal supply. Groundwater quality can be affected by land-use activities occurring at or near land surface. These activities include irrigation of vegetated landscapes and the use of septic systems to dispose of wastewater. Groundwater quality can also be affected by declining water levels, as there is the potential to change the distribution of flow from underlying aquifers to wells. Historic and current water-quality data was used to determine which constituents had relatively high concentrations compared to water-quality thresholds and if these constituent concentrations were changing in response to declining water levels. Age-dating isotopes (tritium and carbon-14) were analyzed to determine if modern groundwater recharge is occurring in the Borrego Valley. Major findings of groundwater-quality portion of this study are the following:
- Historic water-quality data showed that in the upper aquifer, total dissolved solids (TDS) and nitrate as N exceeded their respective water-quality thresholds of 500 mg/L (secondary recommended CA-MCL) and 10 mg/L. Currently, the source of this nitrate is unknown.
- TDS and sulfate were the only constituents that showed increasing concentrations with simultaneous declines in water levels.
- TDS and nitrate concentrations were generally highest in the upper aquifer and in the northern portion of the Borrego Valley, where agricultural activities are primarily concentrated.
- Age-dating isotopes indicated that very little groundwater recharge is occurring under current climatic conditions and that the vast majority of natural recharge is occurring adjacent to the mountain fronts.
Borrego Valley Groundwater References
Borrego Water District, 2009. Integrated Water Resources Management Plan.
California Department of Water Resources, 1998. San Diego County Land use survey, accessed January 31, 2014, at http://www.water.ca.gov/landwateruse/lusrvymain.cfm.
California Department of Water Resources, 1984b. Evaluation of future operations of the Borrego Valley ground water basin: California Department of Water Resources Technical Information Record 1335-11-B-2, by P. Louie and H. Iwanaga.
Dawson, B.J.M., and Belitz, Kenneth, 2012. Status of groundwater quality in the California Desert Region, 2006-2008—California GAMA Priority Basin Project: U.S. Geological Survey Scientific Investigations Report 2012-5040, 110 p.
Dorsey, R.J., 2002. Stratigraphic record of Pleistocene initiation and slip on the Coyote Creek fault, Lower Coyote Creek, southern California, in Barth, A.,ed., Contributions to Crustal Evolution of the Southwestern United States: Boulder, Colorado, Geological Society of America Special Paper 365, p. 251-269.
Durbin, Timothy J.; Bond, Linda D., 1988. FEMFLOW3D; a finite-element program for the simulation of three-dimensional aquifers; version 1.0, U.S. Geological Survey Open-File Report 97-810, 338 p.
Faunt, C. C., Stamos, C. L., Flint, L. E., Wright, M. T., Burgess, M. K., Sneed, M., Brandt, J., Martin, P., and Coes, A. L., 2015. Hydrogeology, Hydrologic Effects of Development, and Simulation of Groundwater Flow in the Borrego Valley, San Diego County, California: U.S. Geological Survey Scientific Investigations Report 2015-5150, DOI: 10.3133/sir20155150
Henderson, Thomas W., 2001. Hydrogeology and Numerical Modeling of the Borrego Valley Aquifer System. Masters Thesis, San Diego State University, 520p.
Hogan, C.M., 2009. California Fan Palm: Washingtonia filifera, in Stromberg, Nicklas, ed., GlobalTwitcher.com.
Hunt, C. B. 1967. Physiography of the United States. W. H. Freeman, San Francisco, Calif. 480 pp.
Mathany, T.M., Wright, M.T., Beuttel, B.S., and Belitz, Kenneth, 2012. Groundwater-quality data in the Borrego Valley, Central Desert, and Low-Use Basins of the Mojave and Sonoran Deserts study unit, 2008-2010: Results from the California GAMA Program: U.S. Geological Survey Data Series 659, 100 p.
Mitten, H. T.; Lines, G. C.; Berenbrock, Charles; Durbin, T. J., 1988. Water resources of Borrego Valley and vicinity, San Diego County, California; Phase 2, Development of a ground-water flow model, USGS Water-Resources Investigations Report 87-4199, 32 p.
Moyle, Jr., W.R., 1988. Water Resources of Borrego Valley and Vicinity, California: Phase 1, Definition of Geologic and Hydrologic Characteristics of the Basin, U.S. Geological Survey Open-File Report 82-855, 43p.
Netto, Steven Paul, 2001. Water Resources of Borrego Valley, San Diego County, CA. Masters Thesis, San Diego State University, 442p.
Subitzky, Seymour (editor), 1985. Selected papers in the hydrologic sciences, U.S. Geological Survey Water Supply Paper 2270, 120 p.
Thorne, James, Ryan Boynton, Lorraine Flint, Alan Flint, and Thuy-N'goc Le (University of California, Davis and U.S. Geological Survey). 2012. Development and Application of Downscaled Hydroclimatic Predictor Variables for Use in Climate Vulnerability and Assessment Studies. California Energy Commission. Publication number: CEC-500-2012-010.
U.S. Census Bureau, 2010. 2010 Census, General Population and Housing Characteristics, Borrego Springs CDP, California. Accessed http://factfinder2.census.gov/main.html on June 27, 2011.
U.S. Census Bureau, 2000. 2000 Census, General Population and Housing Characteristics, Borrego Springs CDP, California. Accessed http://factfinder2.census.gov/main.html on June 27, 2011.
Wright, M.T., Fram, M.S., and Belitz, Kenneth, 2015. Geochemical conditions and the occurrence of selected trace elements in groundwater basins used for public drinking-water supply, Desert and Basin and Range hydrogeologic provinces, 2006-11-California GAMA Priority Basin Project: U.S. Geological Survey Scientific Investigations Report 2014-5173, 48 p.